This invention relates to a medical diagnostic ultrasound catheter and method for position determination. In particular, deformation of a catheter is measured locally to determine the position of a transducer array on the catheter.
Catheters are used for ultrasonic examination of the heart or the vascular system. A transducer array of piezoelectric elements is positioned on the catheter. The catheter is inserted through the circulatory system so that the transducer array is positioned near or within the heart of a patient. However, bending and twisting of the catheter results in ambiguity of the position of the imaging scan plane. Without information on the orientation of the transducer array, a physician relies on image recognition. The images may be from different viewpoints and appear upside down or out of position with respect to the physician""s intuitive understanding of the anatomy.
U.S. Pat. No. 5,876,345 to John W. Eaton et al. discloses two different structures and associated methods for identifying a position of an imaging array on a catheter. In one method, data obtained from an ultrasound scan is used to determine the direction and amount of motion that the arrays have traveled. In the second method, an absolute position sensor, such as a magnetic position sensor, is used to determine the location of the imaging array.
Other types of sensors have been used on colonoscopes. In U.S. Pat. No. 5,728,044, Shan discloses placing strain gauges on a sensor device. Strain gauges are used for torsional and bending measurements. The sensor device is inserted within a colonoscope. However, for imaging calculations, Shan suggests using a sensor device without torsional strain gauges at Col. 6, lines 16-21.
The present invention is defined by the following claims, and nothing in this section should be taken as a limitation on those claims. By way of introduction, the preferred embodiment described below includes a method and catheter for determining a position of the catheter within the cardiovascular system. Local bending and twisting is measured at multiple locations along the catheter. By integrating the measurements, the position and orientation of the catheter is determined. Based on the catheter position information, the location and orientation of an ultrasound transducer array connected with the catheter is known. The imaging array position and orientation information may be used to assist a physician in determining the tissue structure or fluid being scanned and/or assist in the accurate generation of three-dimensional representations.
In one aspect, a medical diagnostic ultrasound imaging catheter for determining a catheter position within a cardiovascular system is provided. A flexible catheter rod comprises a shaft portion and a distal end portion. An ultrasound transducer operatively connects with the distal end portion. A plurality of local deformation sensors are spaced along the catheter rod.
In a second aspect, a method for determining a position of a medical diagnostic ultrasound imaging catheter within a cardiovascular system is provided. A local deformation is measured at each of a plurality of locations along the catheter. The local deformation measurements are integrated, and a position on the ultrasound transducer array is determined as a function of the integrated local deformation measurements.
Further aspects and advantages are discussed below in conjunction with the preferred embodiments.